Since the advent of motor vehicles with automatic transmissions using transmission fluids, there has been a need to provide filtered fluid to the automatic transmission assembly. This is because an automatic transmission assembly includes frictional units that couple rotatable members to one or more planetary gear set members, and typically includes one or more fluid actuating devices such as a piston in order to engage and disengage the frictional units, for example. Such an automatic transmission assembly requires not only tight tolerances between components, but also necessarily requires a source of clean lubricating fluid, also known as automatic transmission fluid, for effective and efficient operation.
Various transmission fluid sump filters have been devised to provide a source of automatic transmission fluid that is free of debris or other material deleterious to the proper operation of motor vehicle automatic transmissions. The current desire to minimize the size of sump areas, due to the general desire to reduce the size of all motor vehicle components to lighten motor vehicles for environmental and fuel consumption concerns is at odds with providing a space of sufficient magnitude for a filter surface area sufficient to provide for a source of clean transmission fluid for the serviceable life of the vehicle under various operating conditions including in cold weather. In this latter operating condition, it has been found that the higher viscosity and other properties associated with cold flow of transmission fluid creates an undue and disadvantageous pressure differential across the filtration media that may result in damage to the filtration media and/or filtration assembly that affects its operational functionality and operating life. Consequently, there is a need to provide a transmission fluid sump filter assembly that maximizes the filter surface area under the condition of a reduced sump size, and which is effective for filtering transmission fluid over various operating conditions, including cold flow conditions, and yet relatively economical to fabricate, assemble, and install, and otherwise suited to its intended purpose as an automatic transmission sump filter. This need is of particular significance where a transmission fluid sump is configured as a small space and yet the filtering and dirt holding capacity of the sump filter is expected to match or exceed existing sump filters that are not dimensionally constrained over a variety of operating conditions, including cold flow conditions.